It is known that ophthalmic lenses are subjected to various manufacturing steps in order to give them the prescribed ophthalmic properties.
Processes for manufacturing ophthalmic lenses are known that comprise a step of providing an unprocessed or semi-finished lens blank, i.e. a lens blank none of the faces or only one of the faces of which is what is referred to as finished (or in other words a face that defines a simple or complex optical surface).
These processes then comprise one or more steps of turning at least one face of the unprocessed lens blank, in order to obtain what is referred to as a finished face, defining the sought-after optical surface providing the (possibly complex) ophthalmic properties prescribed to the wearer of the ophthalmic lens.
The optical function of an ophthalmic lens is provided mainly by two diopters, corresponding to the front and back faces of the ophthalmic lens. The topography of the surface to be produced depends on the repartition of the function applied between the front and back faces of the lens.
The expression “one or more steps of machining” is here understood to mean steps of what are referred to as roughing, finishing and polishing (machining by surfacing).
The roughing step makes it possible, starting from an unprocessed or semi-finished lens blank, to give those face(s) of the lens blank which are defined as unfinished its (their) surface curvature, whereas the finishing (also called smoothing) step consists in fining the grain or even the precision of the radii of curvature of the faces obtained beforehand and allows the curved surface(s) generated to be prepared (smoothed) for the polishing step. This polishing step is a step of surfacing the roughed or smoothed curved surface(s), and makes it possible to make the ophthalmic lens transparent. The roughing and finishing steps are the steps that set the thickness of the final lens and the radii of curvature of the treated surface, independently of the thickness of the initial object and of its initial radii of curvature.
Generally, the time taken to machine a face of an ophthalmic lens depends on the machine used, on the material and on the complexity of the sought optical surface.
Machining speed is not without effect on the conformity of the optical surface produced to the desired surface. Thus, a very low speed may make it possible to ensure the conformity of a surface but it will affect the productivity thereof. In contrast, a high speed makes it possible to increase productivity but may affect conformity.
Generally, trials need to be carried out for complex surfaces in order to determine an optimal machining speed, this decreasing productivity.
Methods for determining an optimal rotation speed for machining such a lens, independently of the material thereof, from geometric characteristics of the surface to be produced, are known from patent applications WO 2011/083234 and WO 2013/030495.